THE TOUR OF THE CELL

CHAPTER 4

Cell Theory

1) Every organism is composed of one or more

cells

2) Cell is smallest unit having properties of life

(movement, respiration, sensitivity, growth,

reproduction, excretion & nutrition).

3) All cells come from other cells.

Basic Aspects of Cell Structure & Function

The cell:

• Smallest unit of life

• Can survive on its own or has potential to do

so

• Is highly organized for metabolism

• Senses and responds to environment

• Has potential to reproduce

Structure of Cell

All start out life with:

• Plasma membrane

• Region where DNA is stored

• Cytoplasm

Two types:

• Prokaryotic

• Eukaryotic

Fluid Mosaic Model of Cell Membrane (Phospholipid Bilayer)

Main component of cell membranes

Gives the membrane its fluid properties

Two layers of phospholipids

Phospholipid Bilayer

Fluid Mosaic Model

Membrane is a mosaic of• Phospholipids

• Glycolipids

• Sterols

• Proteins

Most phospholipids and some proteins

can drift through membrane

Fluid Mosaic Model

CYTOPLASM

EXTRACELLULAR ENVIRONMENT

Cell Size & Shape

Why Are Cells So Small?

Surface-to-volume ratio

The bigger a cell is, the less surface area there

is per unit volume

Above a certain size, material cannot be

moved in or out of cell fast enough

Defining Features of Eukaryotic Cells

Have a nucleus and other membrane bound organelles

Eukaryotic organisms• Plants

• Animals

• Protistans

• Fungi

Animal Cell Features

Plasma membrane

Nucleus Ribosomes Endoplasmic

reticulum

Golgi body Vesicles Mitochondria Cytoskeleton

Animal Cell

Plant Cell Features

Plasma membrane

Nucleus Ribosomes Endoplasmic

reticulum Golgi body

Cell wall Chloroplast Central

Vacuole Vesicles Mitochondria Cytoskeleton

The Nucleus

Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm

Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells

Components of Nucleus

Nuclear envelope Nucleoplasm Nucleolus Chromosome Chromatin

Nuclear Envelope

Two outer membranes (lipid bilayers)

Pores span bilayer

Nucleolus

Cluster of DNA and proteins Materials from which ribosomal subunits

are built Subunits must pass through nuclear

pores to reach cytoplasm

Chromatin

Cell’s collection of DNA and associated proteins

Chromosome is one DNA molecule and its associated proteins

Appearance changes as cell divides

The Endomembrane System

Group of related organelles in which lipids are assembled and new polypeptide chains are modified

Products are sorted and shipped to various destinations

Endoplasmic Reticulum (ER)

In animal cells, continuous

with nuclear membrane

Extends throughout

cytoplasm

Two regions - rough and

smooth

Protein synthesis (RER),

Lipid synthesis (SER)

Mitochondria

ATP-producing

powerhouses

Double-membrane

system

Carry out the most

efficient energy-

releasing reactions

These reactions

require oxygen

Specialized Plant Organelles

Central Vacuole

Chloroplasts

Central Vacuole

Fluid-filled organelle Stores amino acids, sugars, wastes As cell grows, vacuole expands as a

result of fluid pressure forces cell wall to expand

In mature cell, central vacuole takes up 50-90 percent of cell interior

Chloroplasts

Convert sunlight energy to ATP through photosynthesis

The Cytoskeleton

Present in all eukaryotic cells

Basis for cell shape and internal organization

Allows organelle movement within cells and, in some cases, cell movement

Components of Cytoskeleton

microtubule

intermediatefilament

microfilament

Mechanisms of Movement

Length of microtubules or microfilaments can change

Parallel rows of microtubules or microfilaments actively slide in a specific direction

Microtubules or microfilaments can move organelles to different parts of cell

Flagella and Cilia

Structures for cell

motility

9 + 2 internal

structure

Dynein arm

Microtubule doublet

Cell Surface Specializations & Junctions

Cell wall• Structural component

that wraps around the plasma membrane

• Occurs in plants, some fungi, some protistans

Cell Junctions

Plants

• Plasmodesmata Animals

• Tight junctions

• Adhering junctions

• Gap junctions

Animal Cell Junctions

Tight junctions

Gapjunction

Adhering junction

Prokaryotic Cells

Archaebacteria and Eubacteria

DNA is NOT enclosed in nucleus

Generally the smallest, simplest cells

No organelles